Interferon gamma (IFN.gamma.) is a pleiotropic cytokine product of lymphocytes (subtype Th-1) and natural killer (NK) cells which plays a critical role in a variety of immunological functions (Farrar, M. A. et al., (1993). The cDNA and amino acid sequences for both murine and human IFN.gamma. have been determined (Gray, P. W. et al., 1983); Rinderknecht, E. et al., 1984). Both the murine and human IFN.gamma. proteins exist as homodimers that are biologically active.
Among IFN.gamma.'s many effects are the induction of a number of antiviral proteins, upregulation of class II MHC expression, a role in B cell maturation, activation of cells to cytotoxic states, and release of mediators of inflammation (Johnson, H. M., 1985). Thus, IFN.gamma. plays an important role in host defense, inflammation and autoimmunity. These activities are induced as the IFN.gamma. molecule interacts in a species-specific manner with a single class of cell surface receptor and an associated cofactor molecule (Pestka, S. et al., 1987). In both mice and in humans, the IFN.gamma. receptor is a single chain glycoprotein of approximately 85-90 kD which has fairly large (&gt;200 amino acids) extracellular and cytoplasmic domains.
An understanding of the structural basis for IFN.gamma. binding to its receptor provides insight into the mechanism by which ligand binding activates signal transduction. Murine IFN.gamma. has been shown to bind to a soluble form of its receptor via both the N-terminus and the C-terminus of the protein (Russell, J. K. et al., 1986; Magazine, H. I. et al., 1988; Griggs, N. D. et al., 1992). While the N-terminus of murine IFN.gamma. binds to the extracellular domain of the receptor (amino acid residues 95-120 of the receptor) (VanVolkenburg, M. A. et al., 1993), the C-terminus of murine IFN.gamma. does not bind to this region of the receptor. A C-terminal peptide of murine IFN.gamma., consisting of amino acid residues 95-133, binds to the membrane proximal region of the cytoplasmic domain of the murine IFN.gamma. receptor (amino acid residues 253-287) and human IFN.gamma. receptor (amino acid residues 252-291) (Szente, B. E. et al., 1994(a); Szente, B. E. et al., 1994(b)). Previous studies have shown that intracellular IFN.gamma. can induce an antiviral state and upregulation of MHC class II molecules in a species nonspecific fashion (Sanceau, J. et al., 1987; Smith, M. R. et al., 1990).
Although it has been known that certain deletions or mutations of amino acids in the C-terminus of the IFN.gamma. molecule can diminish the biological activity of the protein, the discovery of peptides that comprise a portion of the C-terminus sequence of the full-length IFN.gamma. and that retain biological activity was unexpected.